"value is too large for field of 1 byte" after commit 1a47f3f3db665

[nathanchance]

After 1a47f3f (which does not appear to have a corresponding PR), I see an error when building certain Linux kernels:

error: <instantiation>:9:2: error: value of -130 is too large for field of 1 byte.
 jmp 801b
 ^
make[5]: *** [/builds/linux/scripts/Makefile.build:361: arch/x86/kvm/svm/vmenter.o] Error 1

https://elixir.bootlin.com/linux/v6.6.41/source/arch/x86/kvm/svm/vmenter.S#L60

I used cvise --not-c to produce

.macro ALTERNATIVE_2 oldinstr newinstr1  
 .skip (144f-143f) ^ (144f-143f < 145-144) 
 .pushsection ""
143:
 \newinstr1
144:
 .popsection
.endm
.macro FILL_RETURN_BUFFER reg  
 ALTERNATIVE_2 , "mov $0, \reg; 771: 999: .pushsection .discard.intra_function_calls; .long 999b; .popsection;; call 772f; int3; 72: 99: .pushsection .discard.intra_function_calls; .long 99b; .popsection;; call 772f; int3; 772: add $0 * 2, %rsp; dec \reg; jnz 771b; lfence; movq $-1, %gs:pcpu_hot + 6;" 
.endm
.macro CALL_UNTRAIN_RET
 ALTERNATIVE_2 , "call entry_untrain_ret" 
.endm
.macro __UNTRAIN_RET ibpb_feature call_depth_insns
 CALL_UNTRAIN_RET
 ALTERNATIVE_2 , "\call_depth_insns" 
.endm
.macro RESTORE_GUEST_SPEC_CTRL
801:
.endm
.macro RESTORE_GUEST_SPEC_CTRL_BODY
 movl 936(%rdi), %eax
 cmp %gs:x86_spec_ctrl_current, %eax
 je 801b
 mov edx, %edx
 wrmsr
 jmp 801b
.endm
.macro RESTORE_HOST_SPEC_CTRL
 ALTERNATIVE_2 , "jmp 900f" 
901:
.endm
.macro RESTORE_HOST_SPEC_CTRL_BODY
900:
 mov $0x00000048, %ecx
 jmp 901b
.endm
 RESTORE_GUEST_SPEC_CTRL
2: cli
 pop %rdi
 FILL_RETURN_BUFFER %rax 
 RESTORE_HOST_SPEC_CTRL
 __UNTRAIN_RET , "xor %eax, %eax; bts $63, %rax; movq %rax, %gs:pcpu_hot + 6;"
 pop %r12
 pop rbp
 jmp __x86_return_thunk
 RESTORE_GUEST_SPEC_CTRL_BODY
 RESTORE_HOST_SPEC_CTRL_BODY
cmpb $0, kvm_rebooting
 jne 2b

as a reproducer that has no error with GNU as or clang at the parent of 1a47f3f:

$ x86_64-linux-as --version | head -1
GNU assembler (GNU Binutils) 2.42

$ x86_64-linux-gcc -c -o /dev/null vmenter.s

$ clang --version | head -1
ClangBuiltLinux clang version 19.0.0git (https://github.com/llvm/llvm-project.git 0387cd052b081d6bc9856ef756942a5df1a2a301)

$ clang --target=x86_64-linux-gnu -c -o /dev/null vmenter.s

$ clang --version | head -1
ClangBuiltLinux clang version 19.0.0git (https://github.com/llvm/llvm-project.git 1a47f3f3db66589c11f8ddacfeaecc03fb80c510)

$ clang --target=x86_64-linux-gnu -c -o /dev/null vmenter.s
vmenter.s:51:2: error: value of -130 is too large for field of 1 byte.
 jne 2b
 ^

cc @MaskRay

[MaskRay]

The way we compute MCFillFragment sizes has been wrong for a long time. We should relax it like other relaxable fragments. The issue has been exposed by the layout algorithm change.

gas postpones the negative size warning.
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=32638454a77af8cc49471866d658563b83b0fa8d